(1) Field of the Invention
The present invention relates to an exposure method suitable for use in a photolithography process, a method for manufacturing a semiconductor device using the exposure method, and a method for manufacturing a mask (an exposure mask) for use in the exposure method.
(2) Description of Related Art
In recent years, it has become necessary to form a device pattern of an extremely small size over a semiconductor substrate to meet requirements of high speed and high density in the semiconductor device.
Fine patterning of the device pattern has been achieved by shortening a light source wavelength of an exposure apparatus being used in the photolithography process. At present, the rule of the semiconductor device has reached the level of 100 nm or less. Such a size is shorter than the light source wavelength of the exposure apparatus used when transferring a mask pattern in the photolithography process. By way of example, an argon fluoride (ArF) excimer laser used as the light source has a wavelength of 193 nm.
As such, when transferring the mask pattern onto the substrate by the photolithography, if the resolution limit is exceeded, the shape of a tip position, etc. of the pattern transferred onto the substrate varies due to an optical proximity effect such as diffraction, producing a difference between the mask pattern size and the pattern size transferred onto the substrate.
For example, in a wiring process at the time of manufacturing the semiconductor device, there is a case that a mask pattern 102 such as shown in FIG. 15, in which a narrow width portion 100 (for example, 100 nm in width) and a wide width portion 101 (for example, 550 nm in width) are mixedly provided, is transferred onto the substrate. In this FIG. 15, the portion filled with black depicts a portion through which light transmits.
Now, FIG. 14 shows a schematic cross-sectional view illustrating a wiring structure of the semiconductor device.
As shown in FIG. 14, a wiring layer 111 is constituted as including a lower layer 112, a middle layer 113 and an upper layer 114. Here, an interlayer film is omitted in FIG. 14. Further, in FIG. 14, a symbol 115 represents a semiconductor substrate, and a symbol 116 represents a gate pattern, respectively.
In addition, although the wiring layer is constituted as including the middle layer 113 in the above structure, it may also be possible to structure in such a way as to directly connect the lower layer 112 and the upper layer 114, without providing the middle layer 113.
Here, generally, the wiring widths (minimum wiring widths) formed over the respective layers 112, 113 and 114 constituting the wiring layer 111 are mutually different.
For example, as the case may be, the minimum wiring width formed over the lower layer 112 is 100 nm, the minimum wiring width formed over the middle layer 113 is 200 nm, and the minimum wiring width formed over the upper layer 114 is 400 nm.
In the above case, at the layer connecting the lower layer 112 and the middle layer 113, a mask pattern including both the wiring having the line width of 100 nm and the wiring having the line width of 200 nm is to be transferred onto the substrate. Also, at the layer connecting the lower layer 112 and the upper layer 114, a mask pattern including both the wiring having the line width of 100 nm and the wiring having the line width of 400 nm is to be transferred onto the substrate.
For example, when transferring the mask pattern 102 (mask pattern including wiring of different line widths) such as shown in FIG. 15, in which the narrow width portion 100 and the wide width portion 101 are mixedly provided, at a corner portion 103 or the narrow width portion 100 in the mask pattern 102, the resolution limit is exceeded. As a result, as shown in FIG. 16, a pattern (transfer pattern) 104 transferred onto the substrate undesirably comes to have a narrow width portion 105 thicker than a desired size according to the narrow width portion 100 in the mask pattern 102, as well as a corner portion 106 smaller than a desired size according to the corner portion 103 in the mask pattern 102.
To cope with the above problem, there have been proposed a variety of methods to restrain the influence caused by the optical proximity effect. For example, as a method for correcting the difference between the mask pattern 102 such as shown in FIG. 15 and the transfer pattern 104 such as shown in FIG. 16, a technique for performing optical proximity correction (OPC) has been proposed.
The OPC corrects the variations in shape and size of the pattern transferred onto the substrate, either by partially varying a shape in the opposite way to a pattern deformation produced when transferring the mask pattern in advance (for example, by enlarging the corner portion 103 of the mask pattern 102, or making the narrow width portion 100 still narrower), or by providing a dummy pattern.
For example, when transferring the mask pattern 102 such as shown in FIG. 15 onto the substrate, in order to prevent the deformation of the transfer pattern 104 in shape and size such as shown in FIG. 16, a corrected narrow width portion (correction pattern) 107 is formed using the OPC, by intentionally making the narrow width portion 100 of the mask pattern 102 still narrower, as shown in FIG. 17. Also, the corner portion 103 of the wide width portion 101 is intentionally enlarged by adding an auxiliary pattern 108, which is called hammerhead, to the corner portion 103 of the wide width portion 101 in the mask pattern 102 shown in FIG. 15. Specifically, on applying the OPC to a mask pattern 3 such as shown in FIG. 15, a mask pattern 102A after OPC comes to have a shape as shown in FIG. 17.
By transferring such the mask pattern 102A after the OPC onto the substrate, variations of the transfer pattern in shape and size is restrained.
Additionally, as a result of the search of the prior art, the following pamphlet of International Publication No. 01/063653 has been obtained.
According to the pamphlet of International Publication No. 01/063653, in a Levenson phase-shift mask, when a U-shaped mask pattern is transferred, phase contradiction is produced at phase variation, causing a break of the transfer pattern. To solve the above problem, the mask is divided into two, and using such the masks, a technique of performing multiple exposure has been disclosed.